Ionically conductive materials are used in a variety of electrochemical devices including primary batteries, secondary batteries, solar capacitors, sensors, electrochemical displays, etc. A common ionically conductive material is an electrolyte employing a mixture of alkyl carbonate based liquids containing a lithium salt. These materials are able to form passive films around the anode and cathode, which enable the battery to function efficiently. A majority of known ionically conductive electrolytes used in lithium ion batteries are liquids, which may pose problems in battery applications due to leakage. This requires using more expensive metal containers to prevent leakage in addition to raising the cost of manufacturing them. Additionally, such electrolyte materials may also be highly reactive and inflammable, which may pose safety problems particularly if the battery is overcharged to temperatures above 125° C.
Solid electrolyte materials such as polymer electrolytes and gel electrolytes (collectively referred to herein as solid polymer electrolytes or SPEs) have been developed for use as conductive material in battery applications. Solid polymer electrolytes have excellent characteristics including thin film forming properties, flexibility, lightweight, elasticity, and transparency. These materials also do not exhibit the leakage associated with other ionic conductive materials, and may prevent decreases in battery capacity during repeated use and short-circuiting of positive and negative electrode materials. Solid polymer electrolytes may also exhibit high charging/discharging efficiency, which, along with the ability to be formed as films, allows these materials to be used in various types of batteries of different sizes and shapes.
Conventional batteries employing solid polymer electrolyte technology currently use porous poly(vinylidene) fluoride (PVdF) films swollen with organic carbonate solvents. These films, however, may pose flammability hazards and deficiencies due to limited life cycles.
Alternative electrolyte solvents have been sought. Polymers typically have poor ionic conductivities. Polyethylene oxides have ionic conductivities on the order of 10−6 S/cm. Silicone polyethers have been studied as electrolyte solvent candidates, but many silicone polyethers have ionic conductivities less than 10−3 S/cm, which may not be useful for many battery applications, including, for example, lithium ion batteries. Accordingly, there is a need to develop improved electrolyte candidates that overcome the deficiencies of conventional electrolyte technologies.